Formulating preparations for the treatment of hair fibers is a complex task. Taking hair dye preparations as an example, several challenges can be identified.
When the goal is to create a new hair dye preparation, to produce a new hair color (shade), the first challenge may be to actually define the desired shade. Traditionally, this has often been done by comparison with existing shades: “a bit like this one, but warmer/darker/lighter/more ash/less red/etc.” Obviously, this is a highly subjective and imprecise way to specify a desired shade. The person trying to specify the shade is usually not the person responsible for formulating the dye preparation, which can lead to difficulties in communicating and understanding the precise target shade. For example, a customer in a hair salon may be trying to explain a desired shade to a hair stylist or colorist. Or a hair stylist, colorist, or product developer may be trying to communicate a shade to a dye-formulation expert (usually a specialist chemist). This is further complicated due to the poor ability of humans to be able to accurately remember color. Hence even if a hair dye preparation is subsequently produced to deliver exactly the color initially described, it may be that the person who defined the desired shade no longer recognises it as being what they wanted, and request a different color to be produced, which again when they view the actual result of this new hair dye preparation differs again from what they thought they wanted.
Assuming that the target shade can be successfully defined and agreed, the next challenge is to formulate a composition for a dye preparation that will actually achieve this target shade. This is a non-trivial task because of the complex chemical processes involved in dyeing hair. The end result will depend on the chemical and physical interactions between the existing hair, the dye preparation, and the light illuminating the dyed hair. Treatment conditions (for example, temperature and time) will affect these interactions.
A dye formulation expert may choose the individual dye compounds and their concentrations to be used in a hair dye product. A hair stylist/colorist may choose one or more hair dye products and mix them with an oxidizing agent in suitable proportions to achieve a desired shade. Each hair dye product will typically contain several dye compounds. As used herein, in general, a “preparation” can include both a dye product such as may be formulated by a dye formulation expert, typically containing a plurality of dye compounds, and a mixture of such dye products, such as may be mixed together by a professional colorist.
Even with significant experience, it may be difficult for a dye formulation expert or professional colorist to design a dye preparation that achieves precisely the desired target shade. In particular, when developing a new dye preparation in a commercial setting, it is usual for a dye formulation expert to go through a highly iterative process—formulating a test product, testing it on hair, assessing the results and adjusting the formulation based on his/her skill and experience to approach the target shade. This is laborious, expensive, time consuming, inefficient, and inexact. A professional colorist may have more limited options for iteration, because there will usually be only one customer's hair on which to test a preparation and undesired results may need to be corrected by further dyeing. Therefore, colorists tend to take a conservative approach, recommending only incremental changes to hair color, in order to avoid unpleasant surprises and customer dissatisfaction.
In other instances, the goal is not to create a new shade, but to formulate a composition for a hair dye preparation that will achieve the same shade as an old dye preparation, by using different ingredients. This can happen when an existing ingredient becomes scarce, or expensive, or when safety and/or regulatory guidance change, requiring a current composition to be altered. Although the target shade may be easier to specify when it is the same as an old shade, the problems encountered in achieving that shade are the same as discussed above.